This invention concerns a lead-free or substantially lead-free hydrocarbon fuel composition for spark-ignition internal combustion engines comprising a major amount of hydrocarbons boiling in the gasoline boiling range and a minor amount of iron pentacarbonyl sufficient to confer valuable antiknock properties to the fuel composition but insufficient to cause excessive wear in engine parts when the fuel composition is burned in a spark-ignited internal combustion engine.
Fuel compositions often include at least one additive to improve the antiknock properties of the composition. The antiknock properties of a fuel composition are directly related to and often measured by, the octane number rating of the composition. Thus, if the octane number rating of a fuel composition increases, the antiknock properties of that composition improve. Because of the capital investment required to improve the inherent antiknock properties of hydrocarbon based fuel compositions by means of refinery processing techniques, workers in this area have sought over the years to improve the octane number rating of fuel compositions by developing fuel additives which improve fuel antiknock properties. Fuel additives which improve fuel antiknock properties by even a fraction of a single octane number represent a significant development.
In the past, it has been demonstrated that iron pentacarbonyl is a good antiknock agent and as such compares favorably with tetraethyl lead. This compound which is easily and inexpensively made from readily available iron and carbon monoxide has the economic advantage of being inexpensive to produce. However, when a fuel containing it is burned in an internal combustion engine, it has heretofore had the disadvantage of causing unacceptable wear in the engine parts, particularly wear of the piston rings. The abrasive properties of iron pentacarbonyl have thus far effectively prevented its use commercially in motor vehicles. Attempts have been made to solve the wear problem inherent in the use of iron pentacarbonyl as an antiknock agent in hydrocarbon fuels by the use of wear inhibitors. Examples of wear inhibitors which have been tried are described in U.S. Pat. Nos. 2,546,421 and 2,546,422. U.S. Pat. No. 2,542,421 discloses, as preferred inhibitors, the metal enolates including acylacetonates, such as acetylacetonate and propionylacetonates, alkylaminomethylene acetonates, such as methylaminomethylene acetonates and ethylaminomethylene acetonates; the metal salts of carboxylic acids including naphthenates, alkylphthalates, such as butyl phthalate and 2-ethylhexyl phthalate, and alkenyl succinimates; and metal salts of alkylcarbamic acids and their sulfur analogs, such as dibutylcarbamate, dibutyldithiocarbamate, diamyldithiocarbamate and di-(2-ethylhexyl)-dithiocarbamate. Also, organic derivatives of certain of the metalloids, such as triphenyl arsine and triphenyl antimony also reportedly substantially reduce wear. U.S. Pat. No. 2,546,422 discloses organic phosphates as wear inhibitors for iron carbonyl. Still, this material has never found wide-spread commercial use despite the virtues and advantages with which it has seemed to be endowed.